In 1972, a belt driven tape cartridge design (U.S. Pat. No. 3,692,255, issued to Robert A. Von Behren) was introduced for use in the computer industry for digital tape recording. Cartridges commonly in use in 1972 were approximately 100 mm by 150 mm and the magnetic tape was 6.35 mm (0.250 inches) wide. Cartridges of that size and corresponding drive mechanisms are still commercially available. In 1976, smaller data cartridges were developed, as described by Alan J. Richards, Mini Data Cartridge: A Convincing Alternative for Low-Cost, Removeable Storage, Hewlett-Packard Journal, May, 1976. The mini-cartridge size is 63.5 mm by 82.5 mm. Versions of the mini-cartridge are commercially available from a variety of vendors with tape widths varying from 3.81 mm (0.150 inches) to 8.00 mm (0.315 inches). There are several commercially available variations that provide a larger volume to accommodate a longer tape. In general, the cartridges are longer and may have a portion that is wider, but the edgewall that provides access to the magnetic tape remains a standard size. The present patent document is concerned with mini-cartridges, and not larger cartridges as disclosed by Von Behren.
All the variations of mini-cartridges described above have two openings in one edgewall. The first opening provides access to the tape by a magnetic head. The magnetic head travels across the width of the tape, transverse to the direction of tape movement, accessing one track at a time for reading or writing. The second opening provides access to a driven roller (capstan) inside the cartridge by an external drive roller (sometimes referred to as a drive puck) in the drive mechanism. The external drive roller is rotated by an electric motor in the drive mechanism. In full height drives, the external drive roller is typically driven directly by a shaft connected to the rotor of a motor. With sufficient drive height, the motor can be positioned so that part of the motor is beneath or above the magnetic head, but outside the range of travel of the magnetic head. However, there is an ongoing market demand for decreasing the size of tape drives, and in particular a market demand for decreasing the height of tape drives. As drive height decreases, there may be a mechanical interference between the drive motor and the magnetic head. The interference problem is made even worse with cartridges having a tape width of 8.00 mm (0.315 inches), increasing the distance the magnetic head has to travel. Therefore, in newer low-profile (shorter height) drives, the drive motor is typically displaced relative to the drive roller and connected to the drive roller by a belt or by an intermediate roller. For example, see U.S. Pat. No. 5,210,664 issued to Mark W. Perona on May 11, 1993. Belts and intermediate rollers add cost and may slip or cause other speed problems. A direct drive is desirable as the lowest cost and most reliable way of connecting the drive motor to the drive roller. A low-profile drive mechanism is needed that has both a directly driven drive roller and room for full movement of the magnetic head.